This invention relates to a tool break detector and to a method of monitoring cutting tool vibrations to detect significant tool breakage and prevent false alarms on other vibration noise.
In normal machining operations tool break events are not rare, and they can be very frequent under such conditions as heavy cutting of exotic aircraft engine materials with brittle ceramic tools. The timing of such tool break events, particularly with ceramic tools, cannot be reliably predicted. This situation constitutes a major deterrent to several important approaches to increasing metal-cutting procedure productivity. The approach of assigning two machines to one man is currently considered not to be practical when using brittle ceramic tools in heavy machining, or even when using tough carbide tools near the limits of their capabilities, so some of the advantage of two machines per man is lost in necessary reductions in productivity rates of the individual machines. Automated closed-loop machining cannot safely be applied without a reliable tool break detection technique to prevent marring of the workpiece.
The problem of detecting tool breakage has been studied for many years and devices for this application are on the market. Some of these devices monitor feed or spindle power and some monitor feed forces. In general, they are less than totally satisfactory for reasons of cost, slow response, difficulty in mounting arrangements for some machines, and false alarm problems. Nonetheless, the need for this function has been great enough to result in a number of installations, and in plans for their use even in closed loop machining applications of the future. The present tool break detector, to give a few of its properties, has faster response and greater sensitivity than power and force monitoring systems, and is less sensitive to false alarms than existing acoustic emission detection systems that rely solely on detection of the emission produced by tool fracture. It has more capability than the acoustic emission systems for avoiding alarms on tool break events that do not significantly affect cutting conditions, and is more sensitive in detecting significant tool break events when the actual tool fracture emission signal is masked by high cutting noise.